This invention relates to a semiconductor device comprising a heat radiation plate for radiating heat from a semiconductor chip mounted thereon and a ceramic substrate for mounting the heat radiation plate.
Generally, the semiconductor device comprises a semiconductor chip, a heat radiation plate, and a ceramic substrate. The semiconductor chip is mounted on the heat radiation plate having a plurality of corner portions. The heat radiation plate is for radiating heat generated by the semiconductor chip. The heat radiation plate is fixed to the ceramic substrate. For this purpose, a metallize pattern is formed onto the ceramic substrate. The metallize pattern has a contour similar to that of the heat radiation plate. In other words, the metallize pattern is formed so as to have the same shape as the heat radiation plate. Accordingly, the metallize pattern has a plurality of corner portions which corresponds to those of the heat radiation plate. The heat radiation plate is soldered by soldering method onto the metallize pattern.
The ceramic substrate is used for attaching the semiconductor device to a printed wiring board and for electrically connecting the semiconductor chip and electronic parts mounted on the printed wiring board. For this purpose, a plurality of input/output pin terminals are attached to the ceramic substrate and electrically connected to the semiconductor chip. The plurality of input/output pin terminals are inserted into through holes formed in the printed wiring board and are soldered thereto by the use of a soldering device such as a wave solder device.
Soldering process is carried out on one surface of the printed wiring board having a flat shape. As a result, a temperature difference occurs between the one surface and another surface opposite to the one surface. Such a temperature difference causes transformation of the printed wiring board. Namely, the printed wiring board is bent by bending stress caused by the temperature difference. This means that the plurality of input/output pin terminals are fixed on the printed wiring board having a bent shape. The printed wiring board having the bent shape turns back to the printed wiring board having the flat shape on ordinary temperature. As a result, transformation stress is added to the ceramic substrate through the plurality of input/output pin terminals. In particular, the transformation stress concentrates on each corner portion of the metallize pattern. In this event, there is a case that the metallize pattern is peeled from the ceramic substrate at each of the corner portions thereof. As a result, there is a case that the ceramic substrate has a crack.